1998 CT 40 carb adjustment

[Lyman driver]

Hi,
I have a 98 CT40 2 stroke (3 carb) that runs great at speed, but is the worst idling engine I've ever owned. It has always run poorly. It skips and shakes and smells very rich. Anyone know how to set the carbs?

Thanks,
Joe

[boats.net]

Get you a service manual that shows carb adjustment and synchronization.

[Lyman driver]

Agreed, I need a manual.
But I'm on a lake in Northern NH for two weeks and would like an idea as to where to set the idle mixtures as a start point only. I've seen everything from 7/8 of a turn out from bottom to start at 1-1/2 turns and tweak from there. Motor runs fine at high speed. Also, ignition advance control module has been replaced.

[Ken]

Joe,
There's a good chance your rough idle is gum/varnish related if that motor has been allowed to set up for months at a time w/o being run. Try to get yourself a can of Seafoam at local auto parts house and do a shock treatment per my instructions in previous post.
I would set the idle speed adjustment (pilot screws) at one turn for now on all three carbs until you get a manual - it is different for different models (mine calls for 7/8 turn on a 2000 C115).
If you can, completely remove the pilot screws and squirt some Berryman's Chemtool into the seats to dissolve gum/varnish - and clean the ends of the needles.
Also, I would replace the spark plugs after a shock treatment.
Good luck,
Ken K

[Lyman driver]

Ken,

Thanks. I'm told that there is a local auto parts store about 20 miles from here that has Seafoam. I saw your recipe. I guess if I do it early tonight, there will be zero mosquito presence until the smoke clears.

Joe

[Ken]

Joe,
Go ahead and get two cans of Seafoam - one to do the shock treatment and one to add to the fuel tank - 1 oz per gallon of fuel.
Also, try to get a spray can of Berryman's Chemtool. If you can get to any of the jets, remove them and squirt some BC into the seats. This is addition to removing the pilot screw. On my carbs, there is a pilot screw (idle speed fuel/air adjustment), main jet, pilot jet, and pilot air jet. Very confusing, I know, and all carbs are different. On mine, I can get to the pilot screw and main jet only w/o removing the carbs. I took a look at the carb diagram at boats.net catalogue for your motor, and I can't tell if you can get to the jets or not w/o removing the carbs. The jets will be under the brass plugs and are usually at or near the bottom sides of the carb bowls.
Good luck and let us know how you come out,
Ken K

[Lyman driver]

Ken,

I smoked the neighbors and the bugs out. Removed and cleaned all jets and pilots, reassembled and voila, this engine still sucks. It's been like this since day one. The best I can hope for is that some unsuspecting thief steals it. This reaffirms my feelings and position on "Jap junk". I think at the boat show in January, I'm going to replace this with a non-Yamaha 4-stroke. I never met a japanese engine that I liked, except the Yanmar diesel that was in my old 36 foot sloop. That was an engine!! Thanks for the help, and "Buy American"..

Joe

[Ken]

Joe,
Sorry you are still having problems with your Yammie. Get a Yamaha shop manual (www.yamahapubs.com) and a carb kit (www.boats.net) and do a complete teardown, cleaning, and rebuild of those carbs. When you re-install, synchronize all three according to the manual - and set the pilot screws also.
I share your fustration - took me three years to fix a starter problem (would not engage flywheel about every third hit) on my brand new 2000 C115. No mechanic I talked to (Yamaha or otherwise) could help me - I was just told I had to start replacing parts, like a starter at $450, a flywheel at $650, etc. But my point is, it can be frustrating sometimes trying to fix these outboards - any of them. Don't give up on your Yamaha - it's the best quality out there.
Good luck, and let us know how you come out on that carb rebuild.
Ken K

[Ken]

Joe,
I know this is a long shot and it just came to mind, but check the butterfly valves of the choke to make sure they are not partially closing when not engaged. When open, they should lie perfectly flat in the throat of the carbs. If not, adjust linkage to make so.
Good luck,
Ken K

[Lyman driver]

Ken,

Thanks for the choke butterfly tip. I checked them and they're OK. I ordered the manual today.
I'm going to try a rebuild after vacation. If that doesn't work, I'm gonna shoot it and put it out of its misery.
Thanks again for all yor help.

Joe